# std::set_new_handler

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< cpp‎ | memory‎ | new

Defined in header `<new>` |  |
std::new_handler set_new_handler( std::new_handler new_p ) throw(); |  | (until C++11)
std::new_handler set_new_handler( std::new_handler new_p ) noexcept; |  | (since C++11)

Makes new_p the new global new-handler function and returns the previously installed new-handler.

The new-handler function is the function called by allocation functions whenever a memory allocation attempt fails. Its intended purpose is one of three things:

1) make more memory available,
2) terminate the program (e.g. by calling std::terminate),
3) throw exception of type std::bad_alloc or derived from std::bad_alloc.

The default implementation throws std::bad_alloc. The user can install their own new-handler, which may offer behavior different than the default one.

If new-handler returns, the allocation function repeats the previously-failed allocation attempt and calls the new-handler again if the allocation fails again. To end the loop, new-handler may call std::set_new_handler(nullptr): if, after a failed allocation attempt, allocation function finds that std::get_new_handler returns a null pointer value, it will throw std::bad_alloc.

At program startup, new-handler is a null pointer.

This function is thread-safe. Every call to `std::set_new_handler` synchronizes-with (see std::memory_order) the subsequent `std::set_new_handler` and std::get_new_handler calls. | (since C++11)

### Parameters

new_p | - | pointer to function of type std::new_handler, or null pointer

### Return value

The previously-installed new handler, or a null pointer value if none was installed.

### Example

Run this code

    #include <iostream>
    #include <new>

    void handler()
    {
        std::cout << "Memory allocation failed, terminating\n";
        std::set_new_handler(nullptr);
    }

    int main()
    {
        std::set_new_handler(handler);
        try
        {
            while (true)
            {
                new int[1000'000'000ul]();
            }
        }
        catch (const std::bad_alloc& e)
        {
            std::cout << e.what() << '\n';
        }
    }

Possible output:

    Memory allocation failed, terminating
    std::bad_alloc

### See also

operator newoperator new[] | allocation functions (function)
get_new_handler (C++11) | obtains the current new handler (function)
new_handler | function pointer type of the new handler (typedef)
bad_alloc | exception thrown when memory allocation fails (class)

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